Lithium-ion batteries power the lives of millions of people each day. Due to its lightweight, high energy density, and ability to recharge, this technology is becoming more common in everything from computers and cell phones to hybrids and electric cars. Material handling and airport ground support equipment are also benefiting from these rechargeable batteries.
The technology behind lithium-ion batteries make them a great choice because of their distinct advantages and environmentally-friendly benefits. Do you have any idea how Lithium-ion battery packs are made? The Lithium-ion battery pack is made up of the cell’s having series and parallel connections. In this blog, series and parallel configurations of lithium batteries are discussed.
By configuring these several cells in series we get desired operating voltage. Also the Parallel connection of these cells increase the capacity which directly increase the total ampere-hour (Ah) rating of the battery pack.
INTRODUCTION TO LITHIUM ION BATTERY
A lithium-ion battery, often known as a Li-ion battery, is a rechargeable battery made up of cells in which lithium ions travel from the negative electrode to the positive electrode through an electrolyte during discharge and then back again during charging.
From the anode to the cathode, the electrolyte transports positively charged lithium ions.The movement of lithium ions causes free electrons to develop in the anode, causing a charge to form at the positive current collector. The electrical current then passes from the current collector to the negative current collector, passing through a powered device (cell phone, computer, etc.). The separator prevents electrons from flowing freely inside the battery.
For some devices, a single cell is insufficient. The cells are connected in series to add the voltage of the cells to produce the desired voltage. The cells are connected in parallel to get high capacity by adding ampere-hours to get the necessary capacity (Ah). A battery is the name for this collection of cells.
To achieve the desired voltage and capacity, battery packs are sometimes used in both configurations. The laptop battery uses this configuration, with four 3.6 V Li-ion cells connected in series to produce 14.4 V.Each cell has one another cell connected in parallel to get the double capacity of 6800mAh.
SINGLE CELL CONFIGURATION
The single-cell configuration is said to be the simplest battery pack. This configuration is widely seen in a wall clock, memory backup, and wristwatch. These all are low-power devices, so they use a 1.5 V alkaline battery. As these are all low-power devices, they are powered by a 1.5 V alkaline battery. A single-cell design with a 3.6 V Li-ion battery is also available for mobile phones and tablets. The single-cell configuration of the lithium-ion battery is shown in the image below.
A single Li-ion battery has a nominal voltage of 3.6 V, as we’ve seen. The nominal voltage of a nickel-based battery is 1.2 V, while the nominal voltage of an alkaline battery is roughly 1.5 V. The voltage of the other lithium-based battery ranges from 3.0 to 3.9 V. Li-phosphate has a voltage of 3.2 V, while Li-titanate has a voltage of 2.4 V. Cell voltages of 3.7 V and higher are common in lithium-manganese and other lithium-based systems. The different types of configuration in Lithuim ion Battery is given below/
- SERIES CONFIGURATION
When the voltage of a single cell is insufficient, the series setup is utilized. As seen in the diagram below, the series arrangement is accomplished by connecting the positive of one cell to the negative of another cell. Four 3.6 V lithium-ion cells connected in series to produce 14.4 V, and this arrangement is referred to as 4S since four cells are connected in series.
Depending on the voltage of a single cell, the number of cells can be changed. A Lead-acid battery has a nominal voltage of 2 V, so it requires six cells connected in series to achieve 12 V. Six alkaline batteries, each with a voltage of 1.5 volts, are connected in series to provide 9 volts.
If one of the battery pack’s cells is discharged or damaged, the battery pack will display a warning. This notification is received as a result of the protection board that has been installed.
BMS (Battery Management Systems) or its controller can determine the faulty battery by measuring the voltage at every point of the battery as shown below in the image. The one cell is faulty, which is giving 2.8 V instead of 3.6 V. Due to this, the battery voltage collapses, and the device will shut off sooner with a low-battery message. You can repair your battery pack by replacing this cell.
- PARALLEL CONFIGURATION
If the device requires a larger current but there isn’t enough space for the battery, the cells are connected in parallel to meet the increased current capacity requirements. The parallel arrangement allows the device to accommodate high-current capability into a small footprint. P4 refers to a four-cell parallel design, while P3 refers to three cells joined in a parallel configuration. A P4 arrangement is shown in the image below. The pack’s voltage remains constant, but its current capacity (Ah) is increased.
In a parallel circuit, the cell that develops high resistance or opens is less significant than in a series circuit, but the failed cell will diminish the total current capacity. An electrical short, on the other hand, is more dangerous since the malfunctioning cell drains energy from the other cells, resulting in a fire. Reverse polarisation or dendritic growth cause the short. When the large cell shorts, a fuse is used to disconnect the failing cell. The third cell in the blue box failed in the image below, reducing the capacity to 1500 mAh. The voltage is unaffected, but the total capacity is reduced.
- SERIES-PARALLEL CONFIGURATION
In this configuration, the cells are connected in both series and parallel. The series-parallel design can provide the desired voltage and capacity while taking up the least amount of space. In the figure below, two 3.6 V 3400mAh cells are connected in parallel, doubling the current capacity from 3400mAh to 6800mAh.
As these parallel packs are wired in series, the voltage doubles from 3.6 to 7.2 volts. This battery pack now has a total capacity of 48.96Wh. 2SP2 is the name of this arrangement. When eight cells are joined in a 4SP2 configuration, two cells are connected in parallel, and four packs of this parallel combination are connected in series. This pack’s overall power output is 97.92Wh.
BUILT-IN PROTECTION IN BATTERIES
Some batteries come with safety features within the battery structure. The safety feature of the 18650 Li-ion cells is illustrated in the image below. During normal temperatures, the PTC (positive thermal coefficient) is the resistance that is very low. When the temperature rises above the critical point, the resistance increases, reducing the current flow. PTC comes under normal resistance when the temperature goes below the critical range.
The CID (current interrupt device) is a fuse-type device that permanently cuts off the circuit when the range of cell pressure, temperature, or voltage exceeds its limits. The top disc disconnects from the metallic foil and disconnects the current flow if the internal pressure rises by roughly 1,000kPa. On top, there is a vent that can be opened and closed to release the gas.
Hope, this blog helps you to understand the series and parallel configurations of lithium batteries. We will be back with more informative blogs soon.